Method and apparatus for controlling orientation of needle-like carbon particles in extruded carbon stock

ABSTRACT

A means and method are provided for extruding compositions, particularly for extruding mixes of carbon and/or graphite particles and carbonizable binder, whereby the composition is subjected to greater working than normally encountered in conventional extrusion practices. This extrusion technique results in the elimination of or minimization of the effects of batch interfaces and in better consolidation of the mix. The means and method can additionally be employed to control the orientation of acicular particles in a composition during the extrusion thereof so as to control the properties of the extruded product. In all cases, the extrusion die&#39;&#39;s internal configuration is defined by at least three &#39;&#39;&#39;&#39;working&#39;&#39;&#39;&#39; sections, (which may be interrupted by one or more sections of substantially constant cross section, e.g. cylindrical sections), consisting of a first converging section, then a diverging section, and then a second converging section. When employed in the extrusion of a carbonaceous mix containing needle-like carbon particles, dies of the present invention of appropriate design can be used to produce stock which after baking and graphitizing is characterized by having a transverse to longitudinal average coefficient of thermal expansion (CTE) ratio considerably less than that characteristic of corresponding stock in which the particles are all axially aligned.

United States Patent Juel [ 51 July 11, 1972 [72] Inventor: Leslie II.Juel, 611 Sandlewood Drive,

Lewiston, N.Y. 14092 [22] Filed: Nov. 7, 1969 [21] Appl. No.: 874,849

[52] [1.8. CI. ..264/29, 18/14 V, 23/2092,

25/11, 25/15, 25/17, 264/105, 264/108 [51] Int. Cl ..B29f 3/04, C04b35/54 [58] Field oISearch ..264/l08, 105,29;

[56] References Cited UNITED STATES PATENTS 2,280,022 4/1942 Banigan eta1. ..264/108 2,332,829 10/1943 Parsons et al..... .....264/1082,612,655 10/1952 Mathues ..25/17 2,770,836 11/1956 Hankey... .....2S/173,196,486 7/1965 Shesler et al.. ....264/1 76 3,350,485 10/ 1967 Shesleret a1 ..264/105 OTHER PUBLICATIONS Research and Development on AdvancedGraphite Materials," Volume XLII- Summary Technical Report, WADD TR 6172, Wright-Patterson Air Force Base, Ohio, August 1963, at 76 and 167-173 Primary Examiner-.1 ulius Frome Assistant Examiner-John H. MillerAtmmey-Wallace F. Neyerlin ABSTRACT A means and method are provided forextruding compositions, particularly for extruding mixes of carbonand/or graphite particles and carbonizable binder, whereby thecomposition is subjected to greater working than normally encountered inconventional extrusion practices. This extrusion technique results inthe elimination of or minimization of the effects of batch interfacesand in better consolidation of the mix. The means and method canadditionally be employed to control the orientation of acicularparticles in a composition during the extrusion thereof so as to controlthe properties of the extruded product.

In all cases, the extrusion die 's internal configuration is defined byat least three "working sections, (which may be interrupted by one ormore sections of substantially constant cross section, e.g. cylindricalsections), consisting of a first converging section, then a divergingsection, and then a second converging section. When employed in theextrusion of a carbonaceous mix containing needle-like carbon particles, dies of the present invention of appropriate design can be used toproduce stock which after baking and graphitizing is characterized byhaving a transverse to longitudinal average coefficient of thermalexpansion (CT E) ratio considerably less than that characteristic ofcorresponding stock in which the particles are all axially aligned.

P'A'TENTEBJuu 1 m2 WU 1G 2 INVENTOR. LESLIE H. JUEL METHOD AND APPARATUSFOR CONTROLLING ORIENTATION OF NEEDLE-LIKE CARBON PARTICLES IN EXTRUDEDCARBON STOCK BACKGROUND OF THE INVENTION 1. Field ofthe Invention Thisinvention relates broadly to a method and apparatus for subjecting anextrudable material or composition to a high degree of working whilebeing extruded. It also relates broadly to a method for controlling theorientation of acicular particles in an extrudable material orcomposition so as to control the properties of the extruded product.More particularly this invention relates to a process for the productionand manufacture of carbon and graphite products and to a special meansor apparatus particularly useful in carrying out one of the steps ofsaid production and manufacture, viz. the extrusion step.

2. Description of the Prior Art In the conventional or normal type ofextrusion of green carbon bodies such as electrodes from a mixture ofcarbon and/or graphite particles and a binder, such as pitch, the mix issubjected to essentially continuous reduction in a converging die or diesystem connected directly to the mud cylinder of the press. In theproduction of certain graphite electrodes for steel furnaces, and othergraphite products, such as anodes for brine electrolysis and graphitefor nuclear reactors, a high percentage of the carbon and/or graphiteparticles employed in the mixture are frequently acicular or needle-likein shape. When extruding in a conventional die system, the reductionratio, that is, the ratio of the cross-sectional area of the mud chamberto the cross sectional area of the product to be extruded is frequentlyso great that virtually all of the needle-like particles end up alignedwith their axes parallel to that of the product. This leads to agraphite product which has a relatively high coefficient of thermalexpansion (CTE) in the directionts) perpendicular to, as compared toparallel with, the direction of extrusion and consequently to a graphiteproduct which may not give optimum performance in the par ticularenvironment in which the graphite product is to be used, for examplegraphite electrodes in service on a modern ultra-high powered electricsteel furnace where the thermal shock and thermal stress conditions areparticularly severe.

To control the alignment or orientation of needle-like particles to thedegree that is required or desired in the final graphite electrode whenusing a conventional batch type extrusion press coupled with a singleconverging die, the degree of reduction during extrusion, or, in otherwords, the ratio of the cross-sectional area of the mud cylinder of thepress to the cross-sectional area of the product would have to be sosmall that, particularly in the case of the large-diameter electrodes,only one plus a small-fraction electrode could be extruded from a givencharge to the press. This would mean that the extrusion operation wouldhave to be interrupted much more frequently than when employing aconverging die with a high degree of reduction and that at least everyother electrode extruded would contain a so-called batch interfacegenerated by the mating of two successive batches or charges to thepress. Such interfaces have frequently caused problems in processing,especially when the degree of reduction during extrusion is small, sincethey tend to persist throughout subsequent processing and representpotential regions of weakncss or stress concentration.

A conventional extrusion press with a large mud cylinder, because of itslarge cross-sectional area as compared to the cross-sectional area ofthe electrode to be extruded, permits the extrusion of more than oneelectrode from a given charge and thus minimizes problems connected withbatch interfaces between charges. This, however, suffers thedisadvantage of restricting the degree of freedom over the control ofthe grain orientation in the extruded product since a high degree ofreduction leads to substantially complete or axial alignment of theparticles.

Also, many conventional presses are of the tilting type and have anassociated vertical tamping apparatus. A tamping pressure higher thanthe extrusion pressure is beneficial in the attainment ofa high densityin the final product. In such cases, a separate mechanism is requiredfor high pressure tamping in order to confine the mix, otherwise, thetamping is limited to the normal extrusion pressure of the single diesystem, since, if this pressure is exceeded when the press cylinder isin the ve rtical position required for charging and tamping, thematerial would begin to extrude.

Previous attempts have been made to devise extrusion methods andapparatuses which will accomplish some of the goals and objectives ofthe present invention such as, controlling the transverse to parallel orlongitudinal (T/L) ratio of the CTE of the bodies produced, and U.S.Pat. No. 3,3 50,485 is illustrative of one type of such approach ordevelopment. Appendix VI (pages 167-172) of Technical Documentary ReportNov WADD TR6l-72, Vol. XLII describes another related development.However, the techniques and solutions devised in these references aresubstantially different from the methods and apparatuses devised andemployed in the present invention.

SUMMARY OF THE INVENTION A broad object of this invention is to providea means and method for subjecting an extrudable material to a highdegree of working while being extruded. Another object is to provide ameans and method for extruding mixes of carbon and/or graphite particlesand binder whereby the mix is subjected to greater working and betterconsolidation than normally encountered in conventional extrusionpractices and whereby the structure of carbonaceous (i.e. baked carbonor graphite) stock prepared from the mix is improved. Another object isto permit the use of an increased pressure in extruding such a carbonmixture as compared to that used with a conventional die system. Anotherobject is to provide a means and method for controlling the orientationof acicular particles in a composition during the extrusion thereof soas to control the properties of the extruded product.

A further and more specific object of this invention is to provide ameans and method for controlling the orientation of the coke and/orgraphite particles and binder in a carbonaceous mix during extrusion soas to effect the desired properties in the final product. This latterobjective of the present invention is particularly applicable to theprocessing of coke and/or graphite particles of high quality, i.e. toparticles a high percentage of which contain or possess a needle-likestructure.

Another object is to accomplish the foregoing while still employing aconventional capacity mud chamber and also, if desired, while stillemploying a tilting type press and associated tamping apparatus.

It is a finding of this invention that when processing such acarbonaceous mix containing needle-like coke and/or graphite particlesand a carbonizable binder in a generally longitudinal direction througha forming die of the present invention, the alignment of the particlescan be substantially altered such that the ratio of the transverse tothe longitudinal average coefficient of thermal expansion of theextruded stock, after baking and graphitizing, is reduced from thatcharacteristic of axial alignment. Graphite bodies with such reduced(TIL) CTE ratios or controlled thermal expansion properties may beadvantageous for nuclear reactor applications, for reasons discussed inthe aforesaid U. S. Pat. No. 3,350,485; they may also be advantageouswhen used as thermic electrodes in electric steel furnaces and in otherapplications.

It is an additional finding of the present invention that car bonaceousstock of generally improved structure and typically of higher strength,stemming primarily from the increased working of the mix, and the higherpressures that can be used in extruding it, can be produced when usingprocess techniques and apparatus within the broad scope of the presentinvention, even if the die employed is not so specifically designed asto bring about an alteration in the CTE characteristics and even whenlittle or none of the coke and/or graphite particles employed in the mixbeing processed is of the "needledike" type.

The dies employed to accomplish any of the aforedescribed goals of thepresent invention are all characterized by possessing at least threeworking sections (which sections are also preferably coaxially aligned)comprising a first converging section, then a diverging section and thena second converging section. By a "working" section is meant one that isof varying cross-section throughout its length in contrast to one ofsubstantially constant cross-sectional area. The material passingthrough such a working section experiences external and internal forcesdiffering substantially in magnitude and direction compared to amaterial passing through a section of substantially constantcross-section.

Preferably, the reduction ratios of the cross-sectional areas in each ofthe converging sections are between about 1.25 to l and about I to 1,and the expansion ratio of the cross-sectional areas in the divergingsection is between about I to I.25 and about 1 to l5. In the productionof cylindrical products, the sections are each also preferablycharacterized by possessing smooth interior contours and are also soshaped and designed that a cross-section at any location in each of thesections is circular. (As will be discussed hereinafter, however, thestock being extruded need not always possess such a circularcross-section at any location.) There may be a region or section ofsubstantially constant cross-section (e.g. a substantially cylindricalsection) located before or after one or more of the working sectionsalthough this requirement will depend upon the particular die contourwithin each section and also the particular specific goal being soughtat the time.

The dimensions and contours of the working sections of the die are soregulated as to develop the desired improved structure and physicalproperties. When the mix employed involves particles of the needle-liketype, these particles are substantially aligned with their axes parallelto the axis of the extru sion cylinder upon exiting from the firstconverging section, which is attached directly to the straightcylindrical barrel or mud pot of the extrusion press. From this section,the material enters the diverging portion or "bubble" section of the diesystem where the individual grains or needlelike particles are forced totake a position such that their axes tend to become oriented in a planethat is perpendicular to the axis or direction of extrusion. Thematerial then moves into the second converging section where the finalorientation of the grains or needlelike particles is brought about sothat on the average the angle of inclination that the axes of theseneedlelike particles make with the axis of extrusion will be such thatthe desired CTE characteristics in the final product are achieved. If areduction in the TIL CTE ratio is desired then it is necessary that thereduction ratio of the cross-sectional areas of the stock passingthrough the second converg ing section be less than the reduction ratioin the first converging section. Preferably in such cases thecross-sectional area reduction ratio in the first converging sectionwill be between about 1.25 and about I2 times as great as thecross-sectional area reduction ratio in the second converging section.

The cross-sectional area to which the first section converges will ingeneral be equal to or less than that at the exit end of the entire diesystem, so that a tamping pressure higher than that which would normallybe used when extruding directly through a simple die system having asingle converging section can be employed. The cross-sectional area atthe major diameter of the diverging or bubble" section is at least about1.2 times the cross-sectional area of the product at the exit end of thefinal converging section in order to assure proper functioning of thedie. The contours of the internal surfaces of the various sections ofthe die system are variable but generally consist of smooth surfaces,continuously decreasing or increasing gradually, depending upon whetherthe converging or diverging section is involved. Most frequently thecross-sectional shape of the material being extruded at any givenlocation will be circular. However, in some cases it may be desirablethat the converging and/or diverging sections possess or define othergeometrical configurations, such as to define rectangular, hexagonal orannular cross-sectional shapes.

The overall length of the die system is limited mainly by practicalconsiderations although the design of the diverging or bubble sectionand the rate at which the material being ex truded is forced or passestherethrough should be such that the material exiting from the firstconverging section does not rifle or "shot-gun" through the bubblethereby negating its function.

No baffie plates nor any other types of obstruction are placed withinthe die system, except perhaps a mandrel in case a material of annularcross-section is to be extruded, and the increased working of the mixand/or the control of the alignment of the particles (and consequentlythe achievement of the desired properties) are attained substantiallyentirely by means of the forces applied to the mix by the internalconfiguration of the die system employed and of the various sectionsthereof.

BRIEF DESCRIPTION OF THE DRAWINGS A representative die of preferredconstruction is shown in cross'section in FIG. I. This figure also showsthe internal contours of the various essential sections of the die, aswell as auxiliary apparatus and/or sections used with the die.

FIG. 2 also shows section contours, similar to those shown in FIG. I, ofdies embraced within the invention. FIG. 2 however, is a schematicrather than a cross-sectional view.

DETAILED DESCRIPTION OF THE DRAWINGS & OF THE PREFERRED EM BODIM ENTS InFIG. I the first converging section is shown at A, the diverging orbubble section at B, and the second converging section at C. It will benoted that in section A, the die contour is continuously diminishing andthat the cross-section at any point along its length defines a circle(although the cross-sectional area is changing). The same featureapplies also to sections B and C except that in section B, the contouris frustoconical and there is gradual expansion instead of reduction.

It should be noted that the sections described as A, B and C refer moreto the contours of the die sections rather than the physical parts ofthe die system, these latter now being described in connection with thereference numerals of the drawing.

The mix to be extruded is charged into a cylindrical chamber or mudcylinder" 1 of a conventional hydraulic or mechanical press. The mix isforced through section A by advancing ramhead 2, which is connected tothe mechanically or hydraulically actuated ram 20. (Such a means forforcing the mix into the die sections of the extrusion dies of thepresent invention is greatly preferred over other means, such as ascrewtype extruder.) It will be appreciated that, as illustrated, only aportion of the mud cylinder is shown and that ram 20 and ramhead 2 haveneared the end of their stroke in the direction toward convergingsection A. The press terminates in a flange 1a which is coupled withflange 3a of converging member 3 by means of ring clamp 4. Flange 3b ofmember 3 is coupled to flange 50 at the inlet end of member 5 by meansof ring clamp 6. Member 5, which defines section B, also defines asection of substantially constant cross-sectional area, e. g.cylindrical, at its exit end. Flange 5b, at the exit end of member 5, iscoupled to flange 70, at the inlet end of member 7, by means of ringclamp 8. Member 7 defines section C which converges from its inlet endto a section 7c of substantially constant cross-section, e. g.cylindrical, at its exit end.

It should, of course, be appreciated that the manner in which thesections are joined together in FIG. 1 may be varied, as may also thenumber of members and clamps employed in order to obtain the desiredconfiguration of the entire assembly, the particular way the members arejoined and shown in FIG. I being illustrative only.

The internal configuration of the die shown in cross-section in FIG. 1is repeated schematically in FIG. 2 so as to further and more completelyillustrate dimensions and angles and curves being discussed, which areconsidered representative of the present invention.

The die of FIGS. 1 and 2 is employed in the production ofa cylindricalgraphite product with a diameter of 24 inches. The "mud cylinder" has adiameter of 48 inches (diameter D,). In passing through section A, whichpossesses a length L, of about 30 inches, the stock is gradually reducedto a diameter of about 17 inches (0,). The cross-sectional areareduction ratio of this particular die, therefore, is about 8 to l,which is approximately half the preferred maximum reduction ratio i. e.15.0 to l employed in the first converging section. Diverging section Bhas an average angle of divergence of about (angle X) with respect tothe axis of the die, and the stock being extruded therethrough changesfrom a diameter of about 17 inches at its inlet to a maximum of about 36inches (D (a cross-sectional area expansion ratio of about I to 3.1),over its length L of about 20 inches. (Angle x will generally be betweenabout lS and about 45. The maximum diame ter of 36 inches is maintainedfor a distance L, of about l2 inches in a section of substantiallyconstant cross-section, e. g. a cylindrically shaped portion of member 5(FIG. I) at its exit end, before the stock passes into convergingsection C, wherein diameter D is changed from 36 inches to about 24inches (D,), at an average reduction angle y of l with respect to theaxis of the die, over a linear distance L, of about inches, after whichthe diameter of the stock remains constant for a distance L, of about 30inches in member 70. (The use of a section of substantially constantcross-section, e. g. cylindrical, after the second converging section isa preferred embodiment of the present invention.) Converging section Cthus possesses a cross-sectional area reduction ratio of about L56 to l,which approaches the minimum reduction ratio employed in the section. itwill also be noted that in this particular die design or system thecross-sectional area reduction ratio in the first converging section isabout seven times the cross-sectional area reduction ratio in the secondconverging section.

It will also be noted that the diameter (0,) of the stock (l7 inches)leaving the first converging section of this particular die is less thanthe diameter (0,) of the stock (24 inches) leaving the second convergingsection.v For reasons previously discussed, this is a preferredrelationship in the dies of the present invention, i. e. the diameter ofthe stock leaving the second converging section being greater than(typically at least about 1.2 times as great) or least equal to thediameter of the stock leaving the first converging section.

Another die system embraced within the present invention, and one whichis particularly advantageous for the production of large diameter stockwithout having to resort to larger mud cylinder and extrusion presses,is one wherein the maximum diameter of the stock in the diverging orbubble section (or exiting therefrom ifthe amount of divergence in thebubble sec tion is sufficiently large) exceeds its diameter in the mudcylinder I. For example, the die system may possess an inlet 60 inchesin diameter and the diameter of the stock may be caused to change from60 inches (0,) to 4! inches (0,) in converging section A (across-sectional area reduction ratio of about 2.l to l), to 67 inches (Din diverging section B (a cross-sectional area expansion ratio of about1.0 to 2.7), and finally to inches (D,) in converging section C (across-sectional area reduction ratio of about 2.2 to l).

In such a die system, the average angle of convergence in section A isgenerally smaller than that of section A of H68. 1 and 2, unless lengthL is greatly reduced. The diverging and converging angles 1: and yemployed in sections B and C may be substantially identical to those ofFIGS. 1 and 2, but these too will depend upon and be related to thedimensions L, and 1. of the die in effecting the diameter changesindicated, i.e. from 41 inches to 67 inches and then to 45 inches.

In this embodiment of the invention it will also be noted that thedegree of reduction in the second converging section C slightly exceedsthe degree of reduction (or the reduction ratio in cross-sectional area)of that of the first converging section. A die of this particularconfiguration, although within the scope of the invention, would not beused in order to effect the type of needle-like particle orientation aspreviously described.

Other die systems and configurations may also be employed in carryingout the present invention and in achieving various objectives thereof.The foregoing described die systems, therefore, are not intended to belimitative but rather to be illustrative only of the die configurationsand dimensions which may be used in the present invention.

For example, the die systems of the present invention can advantageouslybe used whenever it is desired to subject an extrudable material to ahigh degree of working. in most instances, however, the minimumcross-sectional area of the stock emerging from the second convergingsection will be at least six square inches. Extruded stock, e. g.carbonaceous, between about and about 3,000 square inches incross-sectionai area is typical of the products produced in the presentinvention.

It should be noted that it is within the spirit of the presentinvention, and may sometimes be advantageous, to employ another dieforming zone after the second converging section. Such a die formingzone would comprise first a diverging section and then a convergingsection, having similar characteristics as sections B and C previouslydescribed. These sections may also each be followed by a section ofsubstantially constant cross-section.

Properties of graphitized products which have been ex truded throughdies (Bubble") of the present invention compared to graphitized productsor controls" which have been conventionally extruded (i. e. using aStandard" single converging section) are set forth in the followingTable. ln Examples l through 6, the carbon aggregate consisted of 45parts of particles, ranging in Tyler screen size from through 3 mesh tojust under 20 mesh, and 55 parts of flour milled to a fineness of5Spercent through 200 mesh. ln Examples 7 and 8 the car bon aggregateconsisted of 45 parts of particles, ranging from one-half inch to justunder 20 mesh Tyler screen size, and 55 parts of flour milled to thesame fineness as in Examples I through 6. In each of the Examples 1through 8, the carbon aggregate was mixed with the indicated number ofparts of binder (coal tar pitch) having a softening point of about 1 l0C, and was extruded at the indicated pressure. (Other carbonizablebinders which may be used in the present invention include variousresins, tars, petroleum pitches and residues. Mixtures of binders mayalso be used.) The extruded products were then baked and graphitized (toabout 2,6()0 C) under identical conditions conventional in the art.

it will be noted that in the Examples using needle coke, and dies of thepresent invention having smaller cross-sectional area reduction ratiosin the second converging section than in the first converging section,i. e. the bubble" dies of Examples 2, 4 and 6, the alignment of theparticles was lessened so that the ratio of the transverse to thelongitudinal average coefficient of thermal expansion (T/l. ratio) ofsaid stock, after baking and graphitizing, was reduced from thatcharacteristic of axial alignment (viz. from that which resulted when astandard" extrusion die was used as in Examples l, 3 and 5).

In the case of Example 8, wherein a non-needle type of coke was used,and a die having a larger cross-sectional area reduction ratio in thesecond converging section than in the first converging section, the T/Lratio of the stock, after baking and graphitizing, was increased fromthat characteristic of axial alignment (Example 7). A die of theseparticular dimensions (Dl-D2-D3-D4)(60-4l-67-45) is thus not suitablefor reducing the T/L ratio; however, like the bubble dies of Examples 2,4 and 6, such a die may be used in the control of particle orientation;is suitable for subjecting an extrudable materialto a high degree ofworking while being extruded; or is suita- TABLE Q" 3 ble for improvingthe structure of carbonaceous stock" in that such a die makes possiblethe exertion of more extrusion pressure upon the carbonaceous mix beingextruded than when using a standard or conventional die, and alsotypically results in product of higher flexural strength and lowerelectri- Q' cal resistivity than a standard" stock product. Such a dieis 5 also embraced within the present invention because it possesses thethree converging, diverging and converging sections e pggg in propersequence as well as several other die features as 3 10 previouslydiscussed.

" The die system of this invention is operated in much the same manneras that employed by those skilled in the art in extruding throughconventional dies. As previously pointed out, however, caution must beobserved to adjust conditions so that the material in the system flowssmoothly and does not shot-gun or rifie through the bubble section.Extra care must also be observed in closely controlling those operatingvariables that affect the rheological characteristics of the mix inorder to assure an axially symmetrical pattern of flow through thesystem as successive batches are charged to the system. A

multiplicity of separately controlled heating coils may be employed tosurround the various sections of the die to assist in this control.

The mix is charged to the mud chamber of the press and is consolidatedby advancing the ram until the die system is 5 figs filled. (To startwith it is necessary to block off the exit end in Standard Bubble D1 D2D1 D2 Dz Dr 60 45 60 41 67 45 Dg/D 3 8 2.2

05% i3 w g Bubble Dr/D-. D: 11. 1 2

Standard Dr Dz Dt 20 40 Dr/Dg an: order to completely fill the bubbleportion of the die system.) Once the die is filled the extrusion can beconducted in the usual manner.

As previously indicated, when using a mix composed of needie-likeparticles and a coal tar pitch binder, and dies with design features aspreviously described, the particles tend to be oriented in the mudchamber of the press with their long axes perpendicular to the axis ofthe cylinder or direction of motion. As the mix progresses through theconverging die, the needle-like particles become aligned with their longaxes mu tually parallel and parallel with the axis of the die. Then asthe 3n 3 2 mix progresses into the diverging portion of the bubble secer40 tion, the needle-like particles tend to become realigned with theiraxes more or less perpendicular to the axis of the die system. Finally,as the mix progresses through the final converging section, the desiredangle of inclination of the needle like particle axes with respect tothe die axis is achieved as defined by the degree of reduction imposed.46 smog, Essentially then, one of the main purposes of many of the psdies embraced within the present invention is to permit the H control ofgrain orientation during extrusion as a means of controlling thecoefficient of thermal expansion (CTE) 50 characteristics in the finalgraphite product. It should be emphasized that the level or magnitude ofthe electrode CTE will be dependent upon the CTE characteristics of theraw material, and that the ratio of the transverse to the longitudinalCTE will be dependent not only on the raw material but also on thespecific dimensions of the various sections of the bubble die system.

Obviously, the properties of the final product can be varied almostinfinitely by proper choice of raw materials and die dimensioning. Whereessentially spherical (rather than needle-like) particles are involvedthe resultant product is essentially isotropic, or more nearly so, butsuperior to a conventionally extruded product because of the greaterworking the mix has experienced. It should also be appreciated that dieswithin the scope of the present invention can also be used for achievingthe production of larger cross-sectional area stock than that of anyparticularly sized mud cylinder that might be on hand and that for suchpurposes the dies can also be used with or without non-needle-likeparticle mixes.

ADVANTAGES SUMM ARIZED The process and apparatus of this invention haveseveral advantages including the following:

Bubble D3 Dr Da/ D 4 Dr D2 24 48 14.6

Dt/D:

as w Standard Dr/ D 2 Bubble D2 D3 D4 17 36 24 Standard D D g v 48 24Apparent density (g./ml.) m .M... Electrical resistivity (lengthwise)(0hm-in.Xl0 CTE f Cr (1)400 0.): LXIOKUUUUHH. TX10 ....t. i.t t t .t..

1 Nolrneedle.

Crosssectional area Binder level (ms/ pts. coke).-..-. Extrusionpressure (p.s.l.) -M

I. They provide means for controlling grain orientation,

hence product properties, while at the same time permitting the use ofpressures higher than those possible through conventional extrusion;

2. They enable the working of the mix more than in conventionalextrusions thereby providing a more highly consolidated product;

. They eliminate or minimize the problems associated with batchseparations in extruding in a conventional manner to achieve the samegrain orientation; and

4. They permit improved efficiency in operations because of the use oflarger batches.

I claim:

1. A method for improving the structure of carbonaceous stock by meansof an extrusion operation wherein the mix employed in making the stockis subjected to a high degree of working while being extruded whichcomprises forcing, by means of a conventional hydraulically ormechanically actuated ram press, the mix, which contains a preponderanceof coke or graphite particles or mixtures thereof and a carbonizablebinder, through a forming die which is free from any obstructions andwhich possesses at least three sections defined by the walls of the diecomprising a first converging section,

then a gradually diverging section possessing no abrupt contour changes,and then a second converging section, the structural integrity of saidcoke or graphite particles being maintained substantially unchangedduring the extrusion operation.

2. A method according to claim I wherein the sections of said formingdie are coaxially aligned.

3. A method according to claim I wherein the minimum cross-sectionalarea of the stock emerging from the second converging section is atleast 6 square inches.

4. A method according to claim 1 wherein the reduction ratios of thecross-sectional areas in each of the converging sections is betweenabout 1.25 to l and about l5.0 to l and wherein the expansion ratio ofthe cross-sectional areas in the diverging section is between about 1 to1.25 and about 1 to 15.

5. A method according to claim 1 wherein the average angle of divergencein the diverging section is between about 15 and about with respect tothe axis of the die.

6. A method according to claim 1 wherein after being forced through thediverging section, the mix is next forced 45 through a section ofsubstantially constant cross-section before being forced through thesecond converging section.

7. A method according to claim 1 wherein the cross-sectional area of thestock leaving the first converging section is equal to or less than thecross-sectional area of the stock leaving the second converging section.

8. A method according to claim 1 wherein the mix is forced through asection of substantially constant cross-section after being forcedthrough the second converging section.

9. A method according to claim 4 wherein the cross-section 12. A methodfor controlling the thermal expansion properties and improving thestructure of carbonaceous stock comprising the step of forcing by meansof a conventional hydraulically or mechanically actuated ram press acarbonaceous mix containing a preponderance of needle-like cokeparticles or needle like graphite particles or mixtures thereof and acarbonizable binder through a forming die which is free from anyobstructions and which possesses at least three sections defined by thewalls of the die comprising a first converging section, then a graduallydiverging section possessing no abrupt contour changes, and then asecond converging section, the reduction ratio of the cross-sectionalareas of the stock entering and leaving the second converging sectionbeing less than the reduction ratio in the first converging section,whereby the alignment of said particles is lessened to such an extentthat the ratio of the transverse to the longitudinal average coefficientof thermal expansion of said stock, after baking and graphitizing, isreduced from that characteristic of axial alignment, the structuralintegrity of said needle-like coke or graphite particles also beingmaintained substantially unchanged during the extrusion operation.

13. A method according to claim 12 wherein the sections of said formingdie are coaxially aligned.

14. A method according to claim 12 wherein the cross-sectional areareduction ratio in the first verging section is between about 1.25 andabout 12 times as great as the crosssectional area reduction ratio inthe second converging section.

15. An apparatus for subjecting an extrudable mass containing apreponderance of particulate material to a high degree of working whilebeing extruded, comprising a cylindrical chamber into which the materialto be extruded is charged, a conventional hydraulically or mechanicallyactuated ram press for forcing the extrudable mass through theapparatus, and a forming die leading from the outlet of the cylindricalchamber, said forming die being characterized by being free from anyobstructions and by possessing at least three sections defined by thewalls of the die comprising a first converging section, then a graduallydiverging section possessing no abrupt contour changes, and the secondconverging section, the reduction ratios of the cross-sectional areas ineach of the converging sections being between about 1.25 to l and about15 to l, and the expansion ratio of the cross-sectional areas in thediverging section being between about 1 to l.25 and about I to l5.

16. An apparatus according to claim 15 wherein the sections of saidforming die are coaxially aligned.

17. An apparatus according to claim 15 wherein the crosssectional areareduction ratio in the second converging section of the forming die isless than the cross-sectional area reduction ratio in the firstconverging section.

18. An apparatus according to claim 16 wherein said coaxially alignedsections are each also characterized by possessing smooth interiorcontours and wherein a cross-section at any location in each of thesections is circular.

19. An apparatus according to claim 17 wherein the crosssectional areareduction ratio in the first converging section of the forming die isbetween about 1.25 and about 12 times as great as the cross-sectionalarea reduction ratio in the second converging section.

2. A method according to claim 1 wherein the sections of said formingdie are coaxially aligned.
 3. A method according to claim 1 wherein theminimum cross-sectional area of the stock emerging from the secondconverging section is at least 6 square inches.
 4. A method according toclaim 1 wherein the reduction ratios of the cross-sectional areas ineach of the converging sections is between about 1.25 to 1 and about15.0 to 1 and wherein the expansion ratio of the cross-sectional areasin the diverging section is between about 1 to 1.25 and about 1 to 15.5. A method according to claim 1 wherein the average angle of divergencein the diverging section is between about 15* and about 45* with respectto the axis of the die.
 6. A method according to claim 1 wherein afterbeing forced through the diverging section, the mix is next forcedthrough a section of substantially constant cross-section before beingforced through the second converging section.
 7. A method according toclaim 1 wherein the cross-sectional area of the stock leaving the firstconverging section is equal to or less than the cross-sectional area ofthe stock leaving the second converging section.
 8. A method accordingto claim 1 wherein the mix is forced through a section of substantiallyconstant cross-section after being forced through the second convergingsection.
 9. A method according to claim 4 wherein the cross-section ofthe mix being extruded at any location in each of the sections iscircular.
 10. A method according to claim 8 wherein after being forcedthrough said section of substantially constant cross-section, the mix isthen forced through another die forming zone comprising first adiverging section and then a converging section.
 11. A method accordingto claim 10 wherein said diverging section and said conVerging sectionare each followed by a section of substantially constant cross-section.12. A method for controlling the thermal expansion properties andimproving the structure of carbonaceous stock comprising the step offorcing by means of a conventional hydraulically or mechanicallyactuated ram press a carbonaceous mix containing a preponderance ofneedle-like coke particles or needle-like graphite particles or mixturesthereof and a carbonizable binder through a forming die which is freefrom any obstructions and which possesses at least three sectionsdefined by the walls of the die comprising a first converging section,then a gradually diverging section possessing no abrupt contour changes,and then a second converging section, the reduction ratio of thecross-sectional areas of the stock entering and leaving the secondconverging section being less than the reduction ratio in the firstconverging section, whereby the alignment of said particles is lessenedto such an extent that the ratio of the transverse to the longitudinalaverage coefficient of thermal expansion of said stock, after baking andgraphitizing, is reduced from that characteristic of axial alignment,the structural integrity of said needle-like coke or graphite particlesalso being maintained substantially unchanged during the extrusionoperation.
 13. A method according to claim 12 wherein the sections ofsaid forming die are coaxially aligned.
 14. A method according to claim12 wherein the cross-sectional area reduction ratio in the firstconverging section is between about 1.25 and about 12 times as great asthe cross-sectional area reduction ratio in the second convergingsection.
 15. An apparatus for subjecting an extrudable mass containing apreponderance of particulate material to a high degree of working whilebeing extruded, comprising a cylindrical chamber into which the materialto be extruded is charged, a conventional hydraulically or mechanicallyactuated ram press for forcing the extrudable mass through theapparatus, and a forming die leading from the outlet of the cylindricalchamber, said forming die being characterized by being free from anyobstructions and by possessing at least three sections defined by thewalls of the die comprising a first converging section, then a graduallydiverging section possessing no abrupt contour changes, and the secondconverging section, the reduction ratios of the cross-sectional areas ineach of the converging sections being between about 1.25 to 1 and about15 to 1, and the expansion ratio of the cross-sectional areas in thediverging section being between about 1 to 1.25 and about 1 to
 15. 16.An apparatus according to claim 15 wherein the sections of said formingdie are coaxially aligned.
 17. An apparatus according to claim 15wherein the cross-sectional area reduction ratio in the secondconverging section of the forming die is less than the cross-sectionalarea reduction ratio in the first converging section.
 18. An apparatusaccording to claim 16 wherein said coaxially aligned sections are eachalso characterized by possessing smooth interior contours and wherein across-section at any location in each of the sections is circular. 19.An apparatus according to claim 17 wherein the cross-sectional areareduction ratio in the first converging section of the forming die isbetween about 1.25 and about 12 times as great as the cross-sectionalarea reduction ratio in the second converging section.